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ERC

PERSIST Report Summary

Project ID: 294517
Funded under: FP7-IDEAS-ERC
Country: Denmark

Mid-Term Report Summary - PERSIST (Bacterial Persistence)

Bacteria produce persister cells that are tolerant to multiple antibiotics because they are hibernating in a dormant state in which the antibiotics cannot eradicate them. Persister cells can thus survive during treatment of infections by antibiotics and cause relapse of disease. With the PERSIST project, we focused on uncovering the molecular mechanisms underlying persister cell formation of the model organism E. coli K-12. In a major breakthrough, we discovered that persister cell formation was controlled by the ubiquitous bacterial regulatory nucleotides tetra and penta-guanosine phosphate [(p)ppGpp]. We discovered that (p)ppGpp activate toxin-antitoxin (TA) loci encoding inhibitors of cell growth. Analysis of single bacterial cells revealed that the level of (p)ppGpp varied stochastically in populations of exponentially growing cells and that the high (p)ppGpp level in these rare cells induced slow growth and persistence. Importantly we observed that (p)ppGpp activation of TA loci required inorganic polyphosphate (polyP) and Lon protease. Similar observations have since been obtained by the analysis of pathogenic organisms (Salmonella and Pseudomomas) thus raising the possibility that the (p)ppGpp-dependent stress response and TAs are pivotal for bacterial persistence in many organisms..

E. coli K-12 codes for at least eleven type II toxin-antitoxin (TA) modules, and we showed previsouly that all these gene loci contribute cumulatively to persistence. Ten of the TA modules encode messenger RNA endonucleases (mRNases) that inhibit translation by catalytic degradation of mRNA while the eleventh module, hipBA, encodes HipA kinase. Because HipA was the first “persister” factor to be discovered, it has been of considerable interest to understanding how HipA inhibits cell growth and induces persistence. We discovered that HipA phosphorylated a conserved serine near the active center of the glutamyl tRNA synthetase (GltX) and thereby inhibited aminoacylation of tRNA-Glu. In turn, inhibition of GltX activated (p)ppGpp synthesis and thereby induced persistence. We showed recently that HipA-induced persistence depended not only on (p)ppGpp but also on PolyP, Lon and the ten mRNase-encoding TA modules. Importantly, single cells analysis showed that the high level of (p)ppGpp caused by activation of HipA did not induce persistence in the absence of TA-encoded mRNases. Thus, our data showed that, surprisingly, slow growth per se does not induce persistence in the absence of TA-encoded toxins, thus supporting the notion that these genes encode central effectors of bacterial persistence.

Taken together our work in the first three years has pushed forward the understanding of molecular mechanisms underlying bacterial persistence and thereby has opened new perspectives for the development of novel drug-target discovery regimes to eradicate or combat diseases caused by bacterial persistence.

Contact

Tine Mathiesen, (Executive accounts manager)
Tel.: +45 35320478
E-mail
Record Number: 179201 / Last updated on: 2016-04-27
Information source: SESAM